#3 EGT Lagging others trouble shooting.

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Fred
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#3 EGT Lagging others trouble shooting.

Post by Fred »

I'm working with my new A&P here in CT on an EGT issue. I'll bullet point what I see, have done, and open to suggestions. I'm thinking the EGT probe port hole needs to be cleaned, but not sure how, or if after you read through what I'm seeing you think differently.

- On run-up #3 EGT lags behind the others by 5-7 mins. Yes it gets up to temp (even higher than the others) after a long time. On shutdown it also cools down 5-10 mins behind the other to. Best I can describe is it lags behind.... Example: others EGT's are are 1,200+ and #3 is at 250. Climbs slowly over 10+ mins to over 1,000.

- A&P pulled the probe that had a bad clamp, cleaned the probe and got the clamp to hold one last time. On start the EGT #3 worked perfectly as normal. 20 min flight and it went south again.

- Ordered new #3 EGT probe and installed as the clamp was shot, and looking like it could be the probe.
- Installed new #3 EGT probe and NO JOY. Same issue temps lagging 5-10+ behind the others, no change.

- Our IA told us to unplug the data connector to the GL behind the MFD and check connections. Performed it and also no joy. A&P thinks we need to consider swaping the GL computer.

Before we do this I wanted to see if anyone else had other thoughts? Since the prob lags I'm thinking blockage in the port hole the EGT is plugged into. Since it is a data connection the lag shouldn't be computer related - not like it's showing zero, or fixed reading...

Any suggestions appreciated.

Thank you,
Fred
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smoss
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Re: #3 EGT Lagging others trouble shooting.

Post by smoss »

The EGT's do odd things if there is a short along the way, and behave in a way you wouldn't think they would. I had a tiny nick in what looked like the insulation only for one of my EGT wires. No problems ever, then one day, EGT for 1 cylinder in flight start's creeping up by about 1 degree per second, starting to get VERY high, and did not change with anything I did such as full rich, or throttle back... just kept creeping up. The plane was running perfectly though, and CHT's were baseline normal. So I'm thinking I'm going to be declaring an emergency soon, disconnect AP to turn around to my home base, and as I start to turn, whammo, EGT drops back to normal. So am very confused, all looked normal again, played with it a bit, then decided to continue on to destination. Well the creep up happened 2 or 3 times more in flight, each time resolved by "shaking" the plane. Upon landing, checked everything under the hood and all looked well, except that the cylinder in question was the one with the tiny insulation nick. I figured a new EGT probe was in store for me. The issue at that time was not reproducible at all on the ground, but soon became evident on the ground, and would do the creep up before starting engine, or after shutdown sometimes. It turned out that if I reached in through the oil filler access hole, and wiggled the connectors for the EGT wires (they sit right forward of there), the problem would immediately resolve. When I finally got around to un-bundling the EGT wires and connectors over there (big plastic connector), unplugged them, cleaned the connections, and replaced them, the EGT has worked perfectly normal for years since then. Moral of the story... problems in the data will not produce a 0 or fixed reading on the G1000, definitely could be a poor connection somewhere.
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Re: #3 EGT Lagging others trouble shooting.

Post by Steve »

The EGT probe projects into the exhaust pipe. If the hole were blocked, you couldn't install it. The fact that a new probe exhibits the same behavior points to a bad/intermittent connection. I would check/clean every connection between the probe and the data computer.

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Re: #3 EGT Lagging others trouble shooting.

Post by Fred »

Thank you Steve! Knowing that it does install completely helps me understand more. I'll check the wiring bundle near the oil filter and the entire loop.

Appreciate the help!

Fred
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Re: #3 EGT Lagging others trouble shooting.

Post by Josh F »

Just had something similar happen to me. 2 hours into a long cross country after 2 months of maintenance and install of ADS-B and new displays the EGT for #2 cylinder spikes to more than 1850. Mixture had been running at 1450 EGT the whole time, and CHTs and oil pressure were all in the green. The engine sounded fine and had no issues during the 5 minutes it took me to get back on the ground. But the EGT for #2 didn’t drop below 1800 even at full rich and idle power. I’m having the field mechanic at KABE check it out tomorrow morning and will report back, but any suggestions would be much appreciated.
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Re: #3 EGT Lagging others trouble shooting.

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Re: #3 EGT Lagging others trouble shooting.

Post by Josh F »

It turned out the #2 EGT probe just died. We’re trying to find a replacement, which may take a day or two, but overall a happy ending.
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Re: #3 EGT Lagging others trouble shooting.

Post by Josh F »

After install of a new EGT probe, I’ve now had the same thing happen again. Any suggestions for what might be happening? Both probes were plugged into the #2 channel on the G1000 when they failed, but the first was actually #4 - someone had plugged the #4 probe into the #2 channel in a prior life. Also, I have gotten some water in the cockpit around the canopy seal over the past few weeks, so I’m wondering if there could have been a short affecting the #2 channel.
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